Merged Ozone Data Set Research Articles

Quasi-biennial modulation of total ozone distribution from equator to polar regions based on observations

The modulation of total ozone (TOZ) by the quasi-biennial oscillation (QBO) not only at the equator, but also at subtropics, middle and high latitudes has long been known. As well, a large number of studies have shown seasonal synchronization and interhemispheric asymmetry of QBO effects in the TOZ in extratropical regions. However, the proposed mechanisms of seasonality and asymmetry as a consequence of the interaction of the quasi-biennial and annual cycles are not well understood. A great problem in comparing model simulations with observations and, hence, in verifying theoretical assumptions about the mechanism of extratropical ozone QBO, is the continually changing phase relationship between the annual and quasi-biennial cycles. This issue is exacerbated by the fact that, as is commonly believed, the wind QBO period is not constant, but varies irregularly from one cycle to another. In this study the influence of the QBO of equatorial stratospheric wind on the global distribution of the TOZ has been analyzed using the SBUV Merged Ozone Data Set (MOD). The investigation of the QBO effects in the TOZ in the subtropics, middle and high latitudes of both hemispheres is based on accounting for the seasonal regularities of the wind QBO, which leads to a limited number of only certain combinations of the quasi-biennial and annual cycles that can be realized. The smaller variability serves to clarify the nature of changes in extratropical ozone. A detailed analysis of the TOZ data for 1970–2021 showed that the interannual TOZ variability at subtropics, middle and high latitudes depends on the alternation of wind QBO cycles of different scenarios. The key moments of the TOZ variations are clearly associated with certain points in time during the downward propagation of the easterly and westerly QBO wind regimes and the seasonally dependent QBO circulation produced by them. These results contradict the general view that it is difficult to isolate the effect of QBO on the TOZ in extratropics because of the irregularly varying QBO period, and can be used in comparing simulated and observed extratropical ozone QBO, as well as in long-term forecast of variations in the TOZ distribution.

Statistical analysis of total column ozone during three recent solar cycles over India

Total column ozone (TCO) distribution and its variation over the Indian region at different stations for the period of about 30 years from 1986 to 2015 are studied. TCO data is taken from the merged ozone data set (MOD) overpass data for 15 different stations over India. The average correlation between TCO and solar proxies such as sunspot number and F10.7 cm solar flux is more than 0.5. We further divided the time series of TCO according to solar cycle as 22nd solar cycle (September 1986 to July 1996), 23rd solar cycle (August 1996 to November 2008) and 24th solar cycle (December 2008 to December 2015) (on going cycle) for a period of 1986–2015. Herein, for the long term trend analysis of TCO, we have removed the seasonal effect by the deseasonalization process, the effects of solar activities, stratospheric waves (quasi-biennial-oscillation-QBO and El Niño–Southern Oscillation-ENSO) by the multifunction linear regression method (MLR). We have compared both the linear trends in TCO which are calculated by the simple linear regression (SLR) and deseasonalised multifunction linear regression (DMLR) analysis. It is found that the direction of the trend in 22nd and the 23rd solar cycle is similar while, it is opposite in the 24th solar cycle. We observed a more negative trend in the 22nd solar cycle and less negative trend in the 23rd solar cycle while the trend is positive in the 24th solar cycle. The results indicate that after the DMLR process, the trend values are decreased by a large factor. Therefore, it is found that the role of natural variability is more than that of the ozone depleting substances (ODS) on long term variability in TCO over India. This statistical analysis provides better analysis of trend variation in TCO series over India. The main objective of this work is to analyze the variations in trend in the TCO with respect to the recent three solar cycles.

Trends in erythemal doses at the Polish Polar Station, Hornsund, Svalbard based on the homogenized measurements (1996–2016) and reconstructed data (1983–1995)

Abstract. Erythemal daily doses measured at the Polish Polar Station, Hornsund (77°00′ N, 15°33′ E), for the periods 1996–2001 and 2005–2016 are homogenized using yearly calibration constants derived from the comparison of observed doses for cloudless conditions with the corresponding doses calculated by radiative transfer (RT) simulations. Modeled all-sky doses are calculated by the multiplication of cloudless RT doses by the empirical cloud modification factor dependent on the daily sunshine duration. An all-sky model is built using daily erythemal doses measured in the period 2005–2006–2007. The model is verified by comparisons with the 1996–1997–1998 and 2009–2010–2011 measured data. The daily doses since 1983 (beginning of the proxy data) are reconstructed using the all-sky model with the historical data of the column ozone from satellite measurements (SBUV merged ozone data set), the snow depth (for ground albedo estimation), and the observed daily sunshine duration at the site. Trend analyses of the monthly and yearly time series comprised of the reconstructed and observed doses do not reveal a statistically significant trend in the period 1983–2016. The trends based on the observed data only (1996–2001 and 2005–2016) show declining tendency (about −1 % per year) in the monthly mean of daily erythemal doses in May and June, and in the yearly sum of daily erythemal doses. An analysis of sources of the yearly dose variability since 1983 shows that cloud cover changes are a basic driver of the long-term UV changes at the site.

Response of trace gases to the disrupted 2015–2016 quasi-biennial oscillation

Abstract. The quasi-biennial oscillation (QBO) is a quasiperiodic alternation between easterly and westerly zonal winds in the tropical stratosphere, propagating downward from the middle stratosphere to the tropopause with a period that varies from 24 to 32 months ( ∼ 28 months on average). The QBO wind oscillations affect the distribution of chemical constituents, such as ozone (O3), water vapor (H2O), nitrous oxide (N2O), and hydrochloric acid (HCl), through the QBO-induced meridional circulation. In the 2015–2016 winter, radiosonde observations revealed an anomaly in the downward propagation of the westerly phase, which was disrupted by the upward displacement of the westerly phase from ∼ 30 hPa up to 15 hPa and the sudden appearance of easterlies at 40 hPa. Such a disruption is unprecedented in the observational record from 1953 to the present. In this study we show the response of trace gases to this QBO disruption using O3, HCl, H2O, and temperature from the Aura Microwave Limb Sounder (MLS) and total ozone measurements from the Solar Backscatter Ultraviolet (SBUV) Merged Ozone Data Set (MOD). Results reveal the development of positive anomalies in stratospheric equatorial O3 and HCl over ∼ 50–30 hPa in May–September of 2016 and a substantial decrease in O3 in the subtropics of both hemispheres. The SBUV observations show near-record low levels of column ozone in the subtropics in 2016, resulting in an increase in the surface UV index during northern summer. Furthermore, cold temperature anomalies near the tropical tropopause result in a global decrease in stratospheric water vapor.

The representation of solar cycle signals in stratospheric ozone – Part 1: A comparison of recently updated satellite observations

Abstract. Changes in incoming solar ultraviolet radiation over the 11-year solar cycle affect stratospheric ozone abundances. It is important to quantify the magnitude, structure, and seasonality of the associated solar-ozone response (SOR) to understand the impact of the 11-year solar cycle on climate. Part 1 of this two-part study uses multiple linear regression analysis to extract the SOR in a number of recently updated satellite ozone datasets covering different periods within the epoch 1970 to 2013. The annual mean SOR in the updated version 7.0 (v7.0) Stratospheric Aerosol and Gas Experiment (SAGE) II number density dataset (1984–2004) is very consistent with that found in the previous v6.2. In contrast, we find a substantial decrease in the magnitude of the SOR in the tropical upper stratosphere in the SAGE II v7.0 mixing ratio dataset (∼ 1 %) compared to the v6.2 (∼ 4 %). This difference is shown to be largely attributable to the change in the independent stratospheric temperature dataset used to convert SAGE II ozone number densities to mixing ratios. Since these temperature records contain substantial uncertainties, we suggest that datasets based on SAGE II number densities are currently most reliable for evaluating the SOR. We further analyse three extended ozone datasets that combine SAGE II v7.0 number densities with more recent GOMOS (Global Ozone Monitoring by Occultation of Stars) or OSIRIS (Optical Spectrograph and Infrared Imager System) measurements. The extended SAGE–OSIRIS dataset (1984–2013) shows a smaller and less statistically significant SOR across much of the tropical upper stratosphere compared to the SAGE II data alone. In contrast, the two SAGE–GOMOS datasets (1984–2011) show SORs that are in closer agreement with the original SAGE II data and therefore appear to provide a more reliable estimate of the SOR. We also analyse the SOR in the recent Solar Backscatter Ultraviolet Instrument (SBUV) Merged Ozone Dataset (SBUVMOD) version 8.6 (VN8.6) (1970–2012) and SBUV Merged Cohesive VN8.6 (1978–2012) datasets and compare them to the previous SBUVMOD VN8.0 (1970–2009). Over their full lengths, the three records generally agree in terms of the broad magnitude and structure of the annual mean SOR. The main difference is that SBUVMOD VN8.6 shows a smaller and less significant SOR in the tropical upper stratosphere and therefore more closely resembles the SAGE II v7.0 mixing ratio data than does the SBUV Merged Cohesive VN8.6, which has a more continuous SOR of ∼ 2 % in this region. The sparse spatial and temporal sampling of limb satellite instruments prohibits the extraction of sub-annual variations in the SOR from SAGE-based datasets. However, the SBUVMOD VN8.6 dataset suggests substantial month-to-month variations in the SOR, particularly in the winter extratropics, which may be important for the proposed high-latitude dynamical response to the solar cycle. Overall, the results highlight substantial uncertainties in the magnitude and structure of the observed SOR from different satellite records. The implications of these uncertainties for understanding and modelling the effects of solar variability on climate should be explored.

OMI total column ozone: extending the long-term data record

Abstract. The ozone data record from the Ozone Monitoring Instrument (OMI) onboard the NASA Earth Observing System (EOS) Aura satellite has proven to be very stable over the 10-plus years of operation. The OMI total column ozone processed through the Total Ozone Mapping Spectrometer (TOMS) ozone retrieval algorithm (version 8.5) has been compared with ground-based measurements and with ozone from a series of SBUV/2 (Solar Backscatter Ultraviolet) instruments. Comparison with an ensemble of Brewer–Dobson sites shows an absolute offset of about 1.5 % and almost no relative trend. Comparison with a merged ozone data set (MOD) created by combining data from a series of SBUV/2 instruments again shows an offset, of about 1 %, and a relative trend of less than 0.5 % over 10 years. The offset is mostly due to the use of the old Bass–Paur ozone cross sections in the OMI retrievals rather than the Brion–Daumont–Malicet cross sections that are now recommended. The bias in the Southern Hemisphere is smaller than that in the Northern Hemisphere, 0.9 % vs. 1.5 %, for reasons that are not completely understood. When OMI was compared with the European realization of a multi-instrument ozone time series, the GTO (GOME type Total Ozone) data set, there was a small trend of about −0.85 % decade−1. Since all the comparisons of OMI relative to other ozone measuring systems show relative trends that are less than 1 % decade−1, we conclude that the OMI total column ozone data are sufficiently stable that they can be used in studies of ozone trends.

Teleconnection between the central tropical Pacific and the Antarctic stratosphere: spatial patterns and time lags

Coupling between the central tropical Pacific (CTP) sea surface temperature (SST) variability and the Antarctic stratosphere known from previous studies is analysed using a lagged correlation method. Monthly mean SST, stratospheric temperatures and zonal winds from the NCEP–NCAR reanalysis and total ozone from the Merged Ozone Data Set over the 1979–2011 period are used. Indices for interannual variability were created and sequential lagged correlations were used to determine the spatial patterns and time lags of the strongest teleconnection. It has been revealed that interannual SST variations in a westward-oriented V-shaped pattern in the CTP region (160–220°E, 30°N–20°S) are associated with statistically significant positive signals in zonally asymmetric region of the Antarctic stratosphere temperature field. Stratospheric pathway dominates in the poleward and downward propagation of the CTP related anomaly in the Southern Hemisphere zonal wind variability. Abrupt modification of the teleconnection patterns in October is accompanied by occurrence of the intense meridional wave train in the lower stratosphere and troposphere. The strongest lagged correlations between the CTP SST index in June and the Southern Hemisphere atmosphere variables in October (r = ±0.7) could be related to the corresponding seasonal peaks in the stationary planetary wave activity. Possible causes of the V-pattern formation and the lagged teleconnection mechanisms are briefly discussed.

Recent changes in total column ozone based on the SBUV Version 8.6 Merged Ozone Data Set

AbstractThe Solar Backscatter Ultraviolet (SBUV) Merged Ozone Data Set (MOD) provides the longest available satellite‐based time series of profile and total ozone from a single instrument type. The data span a 44 year period from 1970 to 2013 (except a 5 year gap in the 1970s). Data from nine independent SBUV‐type instruments are included in the record, one of which is still operating. Although modifications in instrument design were made in the evolution from the Nimbus‐4 Backscattered Ultraviolet instrument to the modern SBUV(/2) model, the basic principles of the measurement technique and retrieval algorithm remain the same, lending consistency to this record compared to those based on measurements using different instrument types. Nevertheless, each instrument has specific characteristics, and known anomalies must be incorporated in the MOD uncertainty estimates. In this study we describe the latest version of the MOD data set based on SBUV data processed using the Version 8.6 algorithm. We assess the measurement consistency across instruments and use this information to assign a drift uncertainty to the MOD. We then fit a multiple regression model to the MOD time series alternately using Equivalent Effective Stratospheric Chlorine (EESC) or linear trend fits over varying time series segments to analyze trends. Regression results indicate a statistically significant positive trend in total ozone outside the tropics based on the EESC proxy fit to the full record, but a linear trend fit to the last 13 years of data does not yield a statistically significant ozone increase.

Total ozone trends and variability during 1979–2012 from merged data sets of various satellites

Abstract. The study presents a long-term statistical trend analysis of total ozone data sets obtained from various satellites. A multi-variate linear regression was applied to annual mean zonal mean data using various natural and anthropogenic explanatory variables that represent dynamical and chemical processes which modify global ozone distributions in a changing climate. The study investigated the magnitude and zonal distribution of the different atmospheric chemical and dynamical factors contributing to long-term total ozone changes. The regression model included the equivalent effective stratospheric chlorine (EESC), the 11-year solar cycle, the quasi-biennial oscillation (QBO), stratospheric aerosol loading describing the effects from major volcanic eruptions, the El Niño–Southern Oscillation (ENSO), the Arctic and Antarctic oscillation (AO/AAO), and accumulated eddy heat flux (EHF), the latter representing changes due to the Brewer–Dobson circulation. The total ozone column data set used here comprises the Solar Backscater Ultraviolet SBUV/SBUV-2 merged ozone data set (MOD) V8.6, the merged data set of the Solar Backscaterr Ultraviolet, the Total Ozone Mapping Spectrometer and the Ozone Monitoring Instrument SBUV/TOMS/OMI (1979–2012) MOD V8.0 and the merged data set of the Global Ozone Monitoring Experiment, the Scanning Imaging Absorption spectroMeter for Atmospheric ChartograpHY and the Global Ozone Monitoring Experiment 2 GOME/SCIAMACHY/GOME-2 (GSG) (1995–2012). The trend analysis was performed for twenty-six 5° wide latitude bands from 65° S to 65° N, and the analysis explained most of the ozone variability to within 70 to 90%. The results show that QBO dominates the ozone variability in the tropics (±7 DU) while at higher latitudes, the dynamical indices, AO/AAO and eddy heat flux, have substantial influence on total ozone variations by up to ±10 DU. The contribution from volcanic aerosols is only prominent during the major eruption periods (El Chichón and Mt. Pinatubo), and together with the ENSO signal, is more evident in the Northern Hemisphere. The signature of the solar cycle covers all latitudes and contributes about 10 DU from solar maximum to solar minimum. EESC is found to be a main contributor to the long-term ozone decline and the trend changes after the end of the 1990s. From the EESC fits, statistically significant upward trends after 1997 were found in the extratropics, which points at the slowing of ozone decline and the onset of ozone recovery. The EESC based trends are compared with the trends obtained from the statistical piecewise linear trend (PWLT) model (known as hockey stick) with a turnaround in 1997 to examine the differences between both approaches. In case of the SBUV merged V8.6 data the EESC and PWLT trends before and after 1997 are in good agreement (within 2 σ), however, the positive post-1997 linear trends from the PWLT regression are not significant within 2 σ. A sensitivity study is carried out by comparing the regression results, using SBUV/SBUV-2 MOD V8.6 merged time series (1979–2012) and a merged data set combining SBUV/SBUV-2 (1979–June 1995) and GOME/SCIAMACHY/GOME-2 ("GSG") WFDOAS (Weighting Function DOAS) (July 1995–2012) as well as SBUV/TOMS/OMI MOD V8.0 (1979–2012) in the regression analysis in order to investigate the uncertainty in the long-term trends due to different ozone data sets and data versions. Replacing the late SBUV/SBUV-2 merged data record with GSG data (unscaled and adjusted) leads to very similar results demonstrating the high consistency between satellite data sets. However, the comparison of the new SBUV/SBUV-2 MOD V8.6 with the MOD V8.0 and MOD8.6/GSG data showed somewhat smaller sensitivities with regard to several proxies as well as the linear EESC trends. On the other hand, the PWLT trends after 1997 show some differences, however, within the 2 σ error bars the PWLT trends agree with each other for all three data sets.

On the regional distinctions in annual cycle of total ozone in the northern midlatitudes

To better attribute the total ozone column (TOC) anomalies observed from the ozone measurements in Ukraine, the climatologies of annual ozone cycle along the latitudinal band 40–60° N with the 30° step in longitude have been analysed. Gridded satellite ozone data based on the merged ozone dataset over the period 1979–2011 are used. The results show that, similar to the known longitudinal dependences of both the total ozone itself and its decadal trends, the annual TOC cycle in the northern midlatitudes is also longitudinally dependent. The higher (lower) regional TOC level is associated with the leading (lagging) development of the annual cycle relative to the zonal mean climatology. Particularly, a 2- to 3-month lead of annual cycle in eastern Asia (120–150° E) in comparison with that in eastern Atlantic (0–30° W) exists. Revealed coupling between regionality and seasonality of the TOC in the northern midlatitudes may be involved in the regional climate variability and deserves further studies with higher temporal and spatial resolution.

Trends and Variability in Total Ozone from a Mid-Latitude Southern Hemisphere Site: The Melbourne Dobson Record 1978–2012

The Australian Bureau of Meteorology maintains a number of long-running Dobson measurement programs, among the few in southern hemisphere mid-latitudes. Data from the Melbourne site (the Melbourne/Airport World Ozone and Ultraviolet Radiation Data Centre (WOUDC) station was originally located at Aspendale, then moved to the city centre, and finally to Melbourne Airport) from 1978 to 2012 have recently been reviewed and re-evaluated. These data are analyzed using multi-linear regression and also by application of an 11-year running mean. Satellite data from the Merged Ozone Dataset are also used for comparison with the Dobson results. We show that the Quasi-Biennial Oscillation (QBO) plays a major role in winter and spring once phase is taken into account by month. We also show that the three so-called “classical” proxies (QBO, solar cycle, and Equivalent Effective Stratospheric Chlorine (EESC)) alone are able to give a good fit to ozone for Melbourne and, more generally, the southern mid-latitudes for most months of the year, in contrast with the case in the northern hemisphere where dynamical variation plays a much more important role. Correspondingly, the smoothed Melbourne Dobson time series shows a high correlation to EESC.

Search for evidence of trend slow-down in the long-term TOMS/SBUV total ozone data record: the importance of instrument drift uncertainty

Abstract. We have developed a merged ozone data set (MOD) for the period October 1978 through June 2006 combining total ozone measurements (Version 8 retrieval) from the TOMS (Nimbus 7, Earth Probe) and SBUV/SBUV2 (Nimbus 7, NOAA 9/11/16) series of satellite instruments. We use the MOD data set to search for evidence of ozone recovery in response to the observed leveling off of chlorine and bromine compounds in the stratosphere. A crucial step in any time series analysis is the evaluation of uncertainties. In addition to the standard statistical time series uncertainties, we evaluate the possible instrument drift uncertainty for the MOD data set. We combine these two sources of uncertainty and apply them to a cumulative sum of residuals (CUSUM) analysis for trend slow-down. For the extra-polar mean between 60° S and 60° N, the apparent slow-down in trend is found to be clearly significant if instrument uncertainties are ignored. When instrument uncertainties are added, the slow-down becomes marginally significant at the 2σ level. For the mid-latitudes of the northern hemisphere (30° to 60° N) the trend slow-down is highly significant at the 2σ level, while in the southern hemisphere the trend slow-down has yet to meet the 2σ significance criterion. The rate of change of chlorine/bromine compounds is similar in both hemispheres, and we expect the ozone response to be similar in both hemispheres as well. The asymmetry in the trend slow-down between hemispheres likely reflects the influence of dynamical variability, and thus a clearly statistically significant response of total ozone to the leveling off of chlorine and bromine in the stratosphere is not yet indicated.